Time travel experiments would probably leave marks or footprints on history

General characteristics of Time Travel Experiments

What should we think of, when talking about the footprints or marks that time travel experiments
would leave behind in history? What should we look for, that might indicate that an event
could be the result of a future time travel experiment? We could devide characteristics of time travel
into general characteristics that would apply to all events,
caused by travel experiments and more specific characteristics
that depend on the theory behind the science and the objectives of the experiment.

General characteristics

Events and consequences without cause or logical explanation

Relationship with the future

Avoids impact on history.

Happen frequently

Documented

Events and consequences without a cause or logical explanation.

Let's say, you could travel back to a past century. That means that you would exist
in a time before you were born and your existence would seem to have no cause, no logical explanation.

Relationship with the future.

Travelers have knowledge of the future and could possibly share that knowledge resulting in prophecy.
Another form of relationship with the future would be for instance the sightings of flying objects
like UFO's, that suposedly use futuristic technology, that we might happen to
invent many years ahead of now.

Avoids impact on history.

With their knowledge of the future and their existence in the past time travelers might
change history with unpredictable and possibly grave consequences.
That might explain why time travelers would not really be interested in revealing themselves,
leaving clear hints, or openly communicate with us.

Happen frequently.

If negative consequences can be limited to a minimum or - even better - completely avoided,
than many, many experiments will be conducted and it should be possible to find evidence, remnants
or footprints of these experiments in every continent and in every century.

Documented

The only way to proof an experiment is by documenting it. Although the resulting document might seem to
have a different purpose (book of prophecy?) it might actually contain certain encrypted, concealed
clues that future scientists can use as proof (bible code?).